From celebrated artists and sporting icons to hill tribe people and menial workers, tens of thousands of mourners are expected to attend today's mass singing of the Royal Anthem in honour of His Majesty King Bhumibol Adulyadej.

As huge crowds started gathering at Sanam Luang for the occasion as early as yesterday evening, Singapore's Prime Minister Lee Hsien Loong paid his respects yesterday to the late King in the Dusit Maha Prasat Throne Hall at the Grand Palace.

Other foreign leaders are also scheduled to arrive to express their condolences, including Malaysian Prime Minister Najib Razak and Cambodian Premier Hun Sen, and will arrive in Bangkok today.

The invitation to join today's mass chanting of the newly arranged version of the Royal Anthem was shared on Wednesday, and within minutes the public response was overwhelming (read more here).

The gates around Sanam Luang have not been closed for over a week as mourners continued pouring into the public square - adjacent to the Grand Palace - to pay their respects to the late King.

In the past couple of days, the black-clad crowds grew even larger in preparation for today's mass singing of the Royal Anthem.

The music will be played by the Siam Philharmonic Orchestra under the baton of Somtow Sucharitkul, featuring over a hundred instruments and another hundred chorus singers.

The mass singing, conceived by national artist and renowned filmmaker and director MC Chatrichalerm Yukol, widely known as Than Mui, will be taped for viewing later on television and at cinemas nationwide.

"I'm so proud to see that Thais from all over the country travelled here for this occasion," said Ms Manee, who did not provide her surname.

The 74-year-old, who lives in the suburbs of Bangkok, could not imagine staying at home while others made the long journey from distant provinces to pay tribute to the late King.

She does not mind the dense, at times suffocating, crowds either. "I'm fortunate enough that I am still able to come here." Overwhelmed with sadness, Ms Manee added she was barely able to touch the food she was offered by volunteers at nearby stalls.

Queuing for a serving of fresh fruit, Pui (real name withheld) said she felt a sense of gratitude on seeing so many Thais united in their love for the late monarch.

Ms Pui traveled from her hometown in Chachoengsao province to pay tribute and listen to the evening prayers for the His Majesty the late King.

Volunteers and charitable people warmed her heart. "We're all here for the same thing, which is to show our love and respect," Ms Pui noted, pointing to the hundreds of people waiting in line for food.

Three hundred kilogrammes of noodles a day are not enough to feed all the mourners who have come to Sanam Luang, said Ms Porn, a khanom krok vendor from Chon Buri province.

As soon as she heard the news of King Bhumibol's death, she phoned her family members and friends, asking for help to set up a food stall in the public square.

"I did it for His Majesty," she said, adding that she usually took part in activities honouring the late King. For the past week, she has been cooking chicken noodles and sweets for Thais gathered in the park.

According to Maj Gen Pongsawat Phanjit, deputy commander of 1st Army Region, massive crowds are expected this weekend which is three-day holiday period from today until Monday.

More than 225,000 people travelled to pay respect to the King over the past week, or about 40,000-50,000 people a day. Last Saturday alone, the crowd grew to over 77,000.

Maj Gen Pongsawat said security checkpoints have been set up to screen participants for today's event and that no private vehicles will be allowed into the area. Authorities concerned are mobilising resources to help manage traffic and facilitate the mourning.

He called on people not to stay overnight at Sanam Luang for safety reasons and urged them to seek accommodation provided by the Bangkok Metropolitan Administration. Maj Gen Pongsawat said there are no reports so far of crime and called on people to alert police or authorities if they suspect anything is amiss.

Meanwhile, Prime Minister Prayut Chan-o-cha yesterday urged government officials to keep in mind that the King is still with the Thai people.

"I'd like to say he has never left us. He's still around, on the ground, in the water, in the air and in everything that he has worked on for us," he told a seminar on state budget planning.

Gen Prayut called on state officials to follow in the King's footsteps in pursuing sustainable development which has been admired worldwide.

He also said that Thailand is at a crossroads and it is time for the country to choose if it will fail or prosper.

"We need to talk to set directions for the future for the country... We need to have our own democracy... The kind that is free of conflicts and balanced with the international community," he said.

Government spokesman Sansern Kaewkamnerd yesterday said Gen Prayut had thanked foreign leaders for joining Thais in mourning the passing of His Majesty the King.